Out of step protection of transmission systems



Oct. l0, 1950 E. L. HARDER OUT-OF-STEP PROTECTION OF' TRANSMISSION SYSTEMS Filed June 19, 1947 Q 600 Rmb.

-WITNESSES2 INVENTOR I Edwin l.. Harder:

ATTORNEY Patented Oct. 10, 1950 OUT OF STEP PROTECTION OF TRANS- MISSION SYSTEMS Edwin L. Harder, Pittsburgh, Pa., assignor to. Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 19, 1947, Serial No.v755,594

16 Claims.

. l My invention relates to a simple and improved system and apparatus for protecting an alternating-current transmission-system against outof-step or out-of-synchronismconditions, either for the purpose of blocking tripping at a point where an opening of the system would ne disadvantageous, orY for the purpose of causing a tripping-operation at a point where it is desired that the two out-of-step portions of the system should preferably be separated from each other by an opening-operation of the breakers.

Heretofore, several different out-of-step relaying systems havebeen known, including a system dependingupon the use of carrier-current relaying, as. described in my Patent 2,144,494

granted January 17, 1927; and a system havingr a complex dependence upon the successive operation of non-directional fault-detectors of diITerent sensitivities, during the progress of an outof-synchronism swing, as described in the Lewis Patent 2,210,680, granted August 6, 1940.

In addition to the'foregoing previously known out-of-step protective relaying systems, a relaying system has been known, but not for out-ofstep detection, in which the phase-angle` zone in which all fault-currents will lie was blocked off by ltwo directionally responsive modified-impedance relays, as shown in Fig. 4 of the Goldsboroughv Patent 2,386,209, granted October 9,

f It is an obj ect of my present invention to provide means for detecting an out-of-synchronism condition by the occurrence of a line-current of faultmagnitude at a phase-angle which is outside of the phase-angle zone in which fault-currents can occur. This out-of-step detection can either be utilized to cause tripping at the station where a separation of the out-of-step portions of the transmission system is desirable, or it can be utilized to. block tripping at another station, and-to continue said blocking action during the time when the linecurrent swings into the region of the phase-angle of fault-currents duringan out-of-synchronism swing of the two portions of a transmission system.k

A more specific object-of my invention is to combine,` with the foregoing out-of-step detection,'a relayingrresponse which insures that the 3-phase line-current isvlarger than a predetermined current-value higher than the maximum load-current value, but not much larger than this value; so as to further distinguish between an. out-of-step swing-condition, in which the current-Values gradually increase, and a faultcondition, in which the current substantially instantaneously reaches its fault-value; this provision being made in addition to the use of zoning directionally responsive elements for marking off the zone or phase-angle band in which fault-currents must lie.

With the foregoing and other objects in View,

. my invention consists of the circuits, systems,

combinations, parts and methods of design and operation, hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Fig. 1 is a simplied diagrammatic view of circuits and apparatus embodying my invention in an illustrative form of embodiment;

Fig. 1A is a simplied schematic diagram of the out-of-step detecting-apparatus such as would be utilized at the breaker I I of the station L in Fig. 1, in case a separation of the system should be desirable at this point, under out-ofstep conditions;

Fig. 1B is a similar View of apparatus such as would be used at the breaker I3 of the station M, in case it should be desirable to block outof-step tripping at this point; and

Fig. 2 is a phase-angle diagram, in polar coordinates,showing the loci of the line-currents which are obtained during two possible diierent out-of-step conditions at the breaker I3 of the station M in Fig. 1, andl also showing the phaseangle zone in which all three-phase faultcurrents must lie.

In Fig. 1, I havel illustrated one kind of transmission-system to which my present invention would be applicable. In Fig. 1, I show three substations of a S-phase, -cyc1e transmission system in which out-of-step-responsive relays would be needed. The three geographically separated substations are indicated by the several B-phase station-buses L, M and N, respectively. The system is indicated as having generating capacity connected thereto at the stations L and N, as indicated schematically by the synchronous generators G1. and GN.

A 3-phase line-section I is indicated as joining the buses L and M, to which said line-section is connected by breakers II and I2, having tripy coils TC11 and T012, respectively. A S-phase tieline 2 is indicated as being connected to the linesection I near the end where the breaker I2 is located. The station M is'further indicated as having two B-phase line-sections 3 and 4 connected thereto, through breakers I3 and It, having the trip-coils TCis and TCM, respectively.

The line-section 3 is represented as connecting the station-bus M to the station-bus N, with a 4breaker I5 at the point of connection with the bus N, said breaker having a trip-coil TC15. The line-section 3 is also represented as having a 3-phase tie-line 5 connected thereto, near the end where the breaker' I5 is located. The station-bus N is also represented as having another line or lines connected thereto, as symbolized by the S-phase line 5, which is connected to the bus N through a breaker I6 having a trip C011 TCie.

In a transmission system such as has just been described, as shown in Fig. 1, it may be supposed that the generating-capacity which is available at the bus N is suicient, in general, to carry the load at the bus M, in case of a failure or nonavailability of the generating-capacity which is connected to the bus L, and it may also be assumed that the available generating-capacity at the bus L Iwould not be suflicient to carry the load at M, in case of a failure or non-availability of the generating-capacity at the bus N. Such situations commonly arise, in interconnected transmission systems such as that which is shown in Fig. 1. It may also be assumed that the electrical center of the transmission system which is shown in Fig. l may be either to the right or left of the intermediate station M, depending upon the distribution of the generating-capacity which is connected to the system at various points, either at the buses L and N as shown, or at the bus M itself (not shown) or at the ends of the various tie-lines 2, 4, and 6.

Fig.V 2 is a phase-angle diagram, in polar coordinates, indicating line-current conditions, such as might exist at the breaker I3 at the intermediate station M, plotting the envelopes of the various possible line-currents with respect to the system-voltage E at the station M.

Under one set of system-conditions, the electrical center of the system is somewhere between the stations L and M, in which case the locus of the ends of the line-current Vectors at the breaker I3 of the station M, during out-of-step systemconditions, might be as indicated by the curve 2l in Fig. 2. Each point in the curve 2I indicates the end of a current-vector which depicts, in polar coordinates, the magnitude and phase of the line-current at the breaker I3, lwith respect to the line-voltage E at the same place. 'Ihe various angles which are marked on the curve 2| in Fig. 2 indicate the phase-angles between the voltage E at the bus M and the internal voltage of the generator GL at the bus L.

During other systemconditions, it is possible that the electrical center of the system will fall somewhere between the buses M and N, in which case the locus of the ends of the line-current vectors at the breaker I3, when plotted with respect to the line-voltage E at the same place, may be something like that which is shown by the curve 22 in Fig. 2, in which case the various phase-angles which are indicated at diierent points around the curve 22, are the phase-angles between the voltage E at the bus M, and the internal voltage of the generator GN at the bus N, in the course of a complete out-of-synchronism swing.

Fig. 2 also depicts a phase-angle zone for three* phase fault-currents, which is illustrated as lying between a 40 lagging phase-angle with respect to the station-M voltage E, and a 100 lagging phase-angle with respect to the same voltage, assuming that the line-section E has an impedance-angle of something like 70, or somewhere near the middle of the phase-angle fault-zone which is included between the straight lines marked 40 and 100, respectively, as indicated by the shaded zone in Fig. 2. Fig. 2 also shows the scale of current-magnitudes. To x our ideas on something denite, it may be assumed that the full-load current iiowing over` the line-section 3 is somewhat less than 500 amperes.

In accordance with my present invention, I have provided two biased directional elements DI and D2, that is, directional elements in which the zero-torque is biased, or at a diflerent phaseangle, than in the directional elements such as have heretofore been commonly used, in connection with protective relays for transmission systems. Ordinarily, a directional element, as heretoore used, has had a zero-torque angle at a linecurrent phase-angle which is displaced from the expected phase-angle of fault-currents. However, I displace this no-torque phase-angle of my directional elements, so that the no-torque ciurent-angle of the element DI is at 40 lagging, as indicated by the straight-line DI in Fig. 2, while the no-torque current-angle of the second directional element D2 is at 100 lagging, as indicated by the straight line D2 in Fig. 2. These angles are just illustrative of any narrow anglerange, leading and lagging with respect to the line or zone in which it is expected that faultcurrents will fall, with any desired margin of safety.

Fig. 1A shows a simplied schematic view of an out-of-step relaying system such as might be utilized at the breaker I I at the bus L, inV accordance 4with my invention, assuming that it is desiredfor the breaker II to be tripped inresponse to any out-of-step swing, so that the two portions of the transmission system will be broken apart' from each other at this point, in any case of loss of synchronism. Fig. 1A shows just the means for responding to out-of-step. conditions, and not' the usual fault-responsive relays such as would be utilized at every relaying point.

For controlling the breaker I I at the station L, as shown in Figs.y l and 1A, I utilize three overcurrent relays IAL, IBL and ICL, one for each of the line-phases A, B and C, and two directional elements, which I have indicated, by Way of example, as phase-A elements marked DIAL and DEAL. In addition, as shown in Fig. 1A, I utilize two auxiliary direct-current relays marked X and XI, in the out-of-step control of the breaker I I.

'Ihe various relays which make up my relaying system, as shown in the accompanying drawing, include various line-responsive relays and various direct-current relays, the various coils and contacts of which are separated into alternatingcurrent circuits and direct-current circuits, respectively, the various circuits being arranged, so far as practicable, after the manner of a schematic diagram or across-the-line diagram. In each case, the main or operating coil of the relay is given a letter-designation or legend, and the same letter-designation or legend is applied to all of the contacts of that relay. The relays and switches are invariably shown in their open or deenergized positions. When a given relay has, in addition to its main or operating Winding, an auxiliary Winding, such as a restraining coil or winding, or a polarizing winding, the auxiliary winding is given the same letter-designation, with a subscript. Arrows or dotted lines are used, to symbolically indicate how the various parts of each relay are connected together. When corresponding elements are utilized in different phases, they are distinguished by suflixes, such as A, B and C, for the diierent phases. In addition. a-

subscript L is' added, to distinguish the lineresponsive relays which are located at the station L.

The alternating-current connections for the various line-responsive relays are shown in Fig. 1. The overcurrent elements IAL, IBL and ICL have similarly marked operating-coils which are energized from the various phases of a bank of linecurrent transformers 3 I, as shown in Fig. l. Each of these relays has a single make-contact, which is marked by the same symbols, as shown in Fig. 1A. The two phase-A directional elements DIAL and D2AL have similarly marked current-responsive coils which are connected in the phase-A circuit of the line-current transformers 3|, and each of these directional elements has a single make-contact which is similarly marked, in Fig. IA. Each of these directional elements DIAL and D2AL is also provided with a voltage-coil, distinguished by the subscript V before the subscript L, in Fig, l, and these two voltage-coils DIAvL and DZAVL are suitably energized from the B--C and A-C relaying-voltages which are supplied by potential-transformers 4I at the station L, as shown in Fig. l, suitable leading impedances ZI and Z2 being connected in series with the respective voltage-coils DIAvL and D2AvL, or other equivalent means being used, to effect the necessary shifting of the no-torque phase-angle of the respective directional elements, so that, when both of the directional elements respond, the phase of the line-current will fall somewhere between the 40 line DI and the 100 line D2 in Fig. 2. I

The direct-current connections for the relaying equipment for the breaker I I at the station L are shown in Fig. 1A. The rst line of this gure shows how the three serially connected makecontacts IAL, IBL and ICL are utilized to energize a conductor 42 from the positive bus (I-). The operating coil of the auxiliary relay X is connected between the conductor 42 -and the negative bus The second line of Fig. 1A shows how the two serially connected make-contacts DIAL and D2AL`are utilized to energize a conductor 43 from the positive bus (-I-), and how the operating coil of the second auxiliary relay XI is connected between the conductor 43 and the negative bus The last line in 3 shows the tripping-circuit connections, utilizing the make-contact X, in series with the back-contact XI, to energize the trip-circuit conductor 44, which continues on, to energize the trip-coil TCn of the breaker II, through the auxiliary make-contact l Ia of the breaker, and thence to the negative bus Fig, 1B shows a much simplified schematic View of protective relaying apparatus for controlling the tripping oi the breaker I3 at the station M, many parts being omitted in the interests of simplicity. In this equipment, as shown in Fig. 1B, the line-responsive relays include three overcurrent elements IA, IB and IC, marked, in Fig. 1B, as having a pick-up value of 600 amperes; three other overcurrent elements IA, IB and IC', marked as having a pick-up value of 800 amperes; and a single phase-A time-delayed overcurrent element IA", marked as having a pick-up value of 400 amperes, and as having a time-delay in its response, as symbolized by a dashpot 50. In addition, the line-responsive relaying equipment, as shown in Fig. 1B, includes the two directional elements DIA and D2A which are similar to the direction elements DIAL and DZAL which are shown in Fig. 1A, except that the directional elements in Fig. 1B have back-contacts DIA and 6 D2A, respectively, and two ymake-contacts DIA and D2A, as marked in accordance with the relaydesignation. 4 f y The current-responsive coils of the several lineresponsive relays of Fig. 1B are energized, as shown in Fig. 1, from a bank of line-current transformers 5I; whilev the voltage-coils DIAv andr D2Av are energized, through the impedances ZI and Z2, from a bank of potential-transformers 6I which are connected to the bus M as shown in Fig. l.

In addition, as shown in Fig. 1B, I utilize two auxiliary direct-current relays marked X2 and T. The direct-current circuits, as shown in Fig. 1B, include the three serially connected make-contacts IA, IB and IC of the 60G-ampere overcurrent relays, which are utilized to energize a conductor 62v from the positive bus (-I-). The three parallel connected back-contacts IA', IB' and IC' of the 80G-ampere overcurrent relays are utilized to connect the conductor 62 to a conductor 63, in Fig. 1B. In addition, a bypassing switch 64 is provided, whereby the conductors 62 and 63 may be directly connected, thus indicating that the 80G-ampere relays IA', IB and IC need not always be utilized. The two back-contacts DIA and D2A of the directional elements are connected in parallel with each other, to join the conductor 63 to a conductor 65, which is utilizedk to energize the operating coil of the auxiliary relay X2, which is connected between the conductor 65 and the negative bus Continuing the description of Fig. 1B, the second line of this gure shows the make-contact X2, of the auxiliary relay of the same designation, utilized to energize a circuit 6B fromy the positive bus (-I), this circuit including a resistor RI, for energizing a circuit 61, which continues on, through a variable resistor R2 and the operating coil of the auxiliary relay T, to a conductor 68 which is connected to the negative bus Relay-coil T and the resistor R2 are shunted by a capacitor C which serves to provide a time-delay of the order of a second, or from l of a second to a second or more, in the dropout time of the relay T.

The third linev of Fig. 1B shows the phase-A tripping-circuit connections, in which three serially connected make-contacts, IA', DIA and D2A, are utilized to energize a conductor 'Il from the positive bus (-I-l. A back-contact of the auxiliary relay T is utilized to connect the conductor II to the trip-circuit conductor I2, from which the circuit continues on, through the trip-coil TCis, and an auxiliary make-contact I3a of the breaker I3, to the negative bus Fig. 1B also shows, by way of illustration of other tripping circuits, a back-up protective tripping-circuit connection, utilizing three serially connected contacts, IA", DIA and D2A, to energize a circuit 13, which may be connected, by a changeover switch 14, either to the conductor II or the trip-circuit conductor 12, so that in the first case, the auxiliary-relay back-contact T will be serially included in the tripping-circuit connections, whereas, in the second case, the back-contact T will not be included, thus indicating that the relay-contact T may, or may not, be included in all of the tripping circuits. It may be noted that the overcurrent contact IA is a time-delayed contact, for back-up protection, andin many cases, its time-delay will be such that the auxiliary-relay contact T will not be needed in series with the back-up element IA",

as will be obvious from the subsequent explanation.

In the operation of my apparatus, it will be noted that an out-of-synchronism swing requires a certain length of time, which may be a second or more, depending upon the time-constants of the particular electrical system. In other Words, it takes time for the system to swing out of step suiiiciently for the line-current to have a phaseangle within the zone which is conned between the response-phases of the two directional elements DI and D2, as indicated in Fig. 2. The out-of-phase swing may start around the locus 22, for example, either clockwise or anti-clockwise, depending upon which end of the system is falling behind the other.

During the out-of-synchronism swing, the linecurrent gradually increases, reaching a maximum value near the 180 point of the swing, this maximum out-of-phase current being usually very considerably higher than the full-load line-current, and considerably higher than minimum fault-current. Long before the system swings as much as 150 degrees out of step, corresponding to current 40 lagging the voltage, the linecurrent between the out-of-phase generator-voltages will, in general, far exceed the maximum load-current value. In accordance with my invention, an out-of-step condition is detected by the occurrence of a current-magnitude higher than the full-load line-current, or, in general, the occurrence of a non-directional fault-condition indication of Some kind, in any current-phase other than the restricted phase-angle zone which is included between the no-torque response-characteristics of the two directional elements, as shown in Fig. 2. If the rst appearance of a current of fault-magnitude occurs within this restricted zone, that is, in the shaded area between the lines DI and D2 in Fig. 2, then that circumstance indicates positively the existence of a fault-condition as distinguished from an out-ofstep swing, but if the line-current builds up to fault-magnitude without falling within the phaseangle zone between the two lines DI and D2 in Fig. 2, then this circumstance can, in general, be taken as a positive indication of an out-of-synchronism condition.

The operation of the Fig. lA equipment for out-of-step tripping of the breaker I I at the station L is as follows. Since an out-of-step condition is a S-phase condition, a response is obtained, in Fig. 1A, to the simultaneous occurrence of a current higher than any load-current, in all three line-phases. Thus, at 600 amperes, which is higher than the full-load current, the overcurrent relays IAL, IBL and ICL respond and energize the auxiliary relay X. IfV this overcurrent condition is the result of the beginning of an out-of-step swing, it will occur at a phase-angle outside of the narrow fault-current phase-angle Zone between the two lines DI and D2 in Fig. 2, which means that both of the biased directional relays DIAL and DEAL will not respond, thus failing to energize the circuit 43 which actuates the second auxiliary relay XI in Fig. 1A. In the third circuit or Fig. 1A, therefore, the make-contact X will pick up, but the back-contact XI will remain closed; thus energizing the trip-circuit, causing the breaker II to open, and segregating the two out-of phase portions of the transmission system.

If, however, the S-phasey overcurrent condition in Fig. 1A had been theV result of a fault, the faultcurrent would have been within the restricted phase-angle zone between the lines DI and D2 in Fig. 2, and both of the directional elements DIAL and D2ArI would have immediately responded, picking up the auxiliary relay XI, and opening the tripping-circuit, at the back-contact XIV which opens faster than the closure of the make-contact X in the tripping-circuit. Tripping would thus have been blocked, insofar as concerns any action of my out-of-step trippingequipment in Fig. 1A, thus leaving the fault to be taken care of by the usual fault-responsive relays (not shown in Fig. 1A), which can be designed and correlated to handle fault-conditions without any regard to out-of-step swings.

In the operation of the Fig. 1B equipment, which illustrates the control of the breaker I3 at the station M, it will be noted that it is desirable for a tripping-operation to be blocked, at this point, in the event of an out-of-step condition, so that the two separated portions of the transmission system may be better able to operate independently of each other, after the system has been cut in two by the operation of the breaker I at the station L.

In Fig. 1B, in the tripping-circuit 1I-I2, a back-contact T is included, which is normally closed, and which opens in response to out-ofsynchronisrn conditions, after a brief time hesitation which may be of the order of 2 or 3 cycles. A time-hesitation, in the opening of the backcontact T, is desirable, although perhaps not always necessary, so as to provide that much additional safeguard against the possibility of an erroneous momentary response of the auxiliary relay T, under fault conditions. If there is a fault, the instantaneously operating fault-responsive relays, such as the SOO-ampere overcurrent-relay IA', and both directional elements DA and D2A, will quickly respond, establishing the trip-circuit, and initiating the opening-operation of the circuit breaker I3.

If there is an out-of-step condition, the relays of Fig. 1B will recognize this by a response of the three 600-ampere overcurrent relays IA, IB and f IC, which will receive their minimum pick-upV current before the line-current builds up to the BOO-ampere setting of the relays IA', IB and IC. At the same time, since the overcurrent condition is now assumed to be the result of an out-ofsynchronism swing, the phase-angle of the current will not be between the lines DI and D2 of Fig. 2, and hence both of the directional elements DIA and D2A will not pick up, so that the backcontact of one of these elements will remain closed, thus completing the energization of the top circuit, 65, in Fig. 1B, and picking up the auxiliary relay X2, which has a response-time of the order of a cycle or a cycle-and-a-half, which is a usual time of response for a relay which is neither extraordinarily fast nor extraordinarily slow.

The picking up of the X2 relay-contact energizes the second circuit, in Fig. 1B, and picks up the second auxiliary relay T, which has a response-time similar to that of the X2 relay, making a total time hesitation of the order of two or three cycles before the back-contact T picks up, after the closure of the three 600-ampere overcurrent-contacts IA, IB and IC. This time-hesitation of two or three cycles is assumed to be too small for the S-phase line-current to increase from 600 amperes to BUO-amperes, in the course of an out-of-synchronism swing, under any expectable system-conditions, so that thetrip-circuit II-12 is blocked or opened, by the liiing of the back-contact T, prior to the closure of the 80G-ampere overcurrent-relay contact IA in the circuit 1I.

The time-hesitation of two or three cycles is also much below the time required for the phaseangle of the line-current to swing to an angle which is within the shaded zone between the lines DI and D2 in Fig. 2, during the course of any out-of-step swing, so that the back-contact T is opened, in the tripping-circuit II-'I2 of Fig. 1B, long before both of the directional contacts DIA and DZA can be simultaneously closed, in this circuit 1I. In this manner, a trippingoperation is blocked, in Fig. 1B, in response to an out-of-synchronism condition, but not blocked in response to a fault-condition which starts out with the DIA and DZA elements both responding.

In the Fig. 1B system, it is necessary for the blocking-contact T to remain open during thel time when the systemis swinging through the phase-angle zone between the lines DI and D2 in Fig. 2, because, in this zone, both of the directional back-contacts DIA and D2A will be open, in the circuit ISS- 65, thus deenergizing the X2 relay which controls the actual blocking-relay T. Consequently, I provide any suitable means which will give the relay T the property of keeping its contact open, for a suitable time-delay period, after the opening of the X2 -contact in its energizing-circuit E6. This time-delay period should be something of the order from 6 cycles to 60 cycles, oreven more, depending upon the time-constant of the system. The required timedelay is the time required for the system to swing between the line-current phases indicated by the lines DI and D2 in Fig. 2.

In the particular system shown in Fig. 1B, the dropout time-delay of the relay T is obtained by means of a su'iciently large capacitor C, which is shunted around the operating-coil T of the relay, and which discharges through the resistor R2 when the normal energizing-circuit 66 is interrupted by the falling out of the make- Contact X2. The time required for the capacitor C to discharge, and hence the falling-out timedelay which is given to the relay T, can be controlled by proper adjustment of the discharging-resistance R2.

As previously indicated, the out-of-step blocking-contact T of Fig. 1B can be included in all, or, only a part, of the tripping-circuits for the trip-coil T013. It is necessary, of course, to utilize the out-of-step blocking-contact T in series with all trip-circuits which would be unable, by themselves, to distinguish between a real faultcondition and the spurious, or only apparent, fault-condition which occurs during an out-ofsynchronism swing. In the case of back-up relay-protection, for example, as is illustrated in the case of the slow-acting 40G-ampere overcurrent-element IA in Fig. 1B, the inherent time-delay in the response of this 40G-ampere relay IA is usually or frequently. longer than any time-delay which is necessary for the system to swing past the zone between the lines DI and D2 in Fig. 2, and hence the circuit 13 of Fig. 1B may safely be connected directly to the circuit 12 through the proper manipulations of the changeover switch 14. However, in those systems in which the out-of-step blocking may be desired, even in the case of the slow-acting 400- ampere relay IA", the changeover switch I4 may be moved to connect the circuit 'I3 to the .circuit 1I, so that the trip-blocking contact T 10 will be included in the tripping-circuit of this slow-acting relay IA".

It will be understood, from the foregoing description, that the G-ampere back-contacts IA', IB' and IC are frequently quite unnecessary, in the circuit 62-63 of Fig. 1B, and hence these contacts may be omitted, as by the closure of the switch 54 in said gure.

In Fig. 1B, I have not made any effort to show all of the protective relaying equipment, even in the case of the phase-A relays which are partially illustrated, and no effort has been made to show the usual phase-B or phase-C relays, which are controlled in the same manner as the phase-A relays.

It is to be understood that the foregoing and other changes may be made, in various details, without departing from the essential spirit of my invention. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

l. Means for detecting an out-of-synchronism condition in an alternating-current line, comprising directionally responsive relaying-means for selectively responding only to line-currents in the region of the phase-angle of fault-currents, substantially' non-directional current-responsive means for selectively responding only to line-currents of higher than load-magnitudes, and out-of-step-responsive relaying-means for responding to a response of said non-directional means and a simultaneous non-response of said directionally responsive relaying-means.

2. A fault-responsive protective relaying system for an alternating-current line, with provision for out-of-synchronism conditions, comprising fault-responsive relaying-means for selectively responding to certain fault-current conditions as distinguished from certain load-current conditions, directionally responsive relaying-means for selectively responding only to linecurrent in the region of the phase-angle of faultcurrents, substantially non-directional currentresponsive means for selectively responding only to line-currents of higher than load-magnitudes, means for promptly performing a protective relaying-operation in joint response to a predetermined response of said fault-responsive relaying-means and a response of said directionally responsive relaying-means, and blocking-means for blocking said protective relaying-operation in response to a response of said non-directional means and a Simultaneous non-response of said directionally responsive 4relaying-means.

3. A fault-responsive protective relaying system for an alternating-current line, with provision for out-of-synchronism conditions, comprising fault-responsive relaying-means for selectively responding to certain fault-current conditions as distinguished from certain load-current conditions, directionally responsive relaying-means for selectively responding only to line-currents in the region of the phase-angle of fault-currents, substantially non-directional current-responsive means for selectively responding only to line-currents of higher than load-magnitudes, means for promptly performing a protective relaying-operation in joint response to a predetermined response of said faultresponsive relaying-means and a response of said directionally responsive relaying-means, blocking means for blocking and protective relayingoperation in response to a response of said nondirectional means and a simultaneous non- 11 response of said directionally responsive relaying-means, and means for establishing a blockcontinuation which endures during the time when the line-current swings into the region of the phase-angle of fault-currents.

4. A fault-responsive*protective relaying system for an alternating-current line, with provision for out-of-synchronism conditions, comprising fault-responsive relaying-means for selectively responding to certain fault-current conditions as distinguished from certain load-current conditions, directionally responsive relaying-means for selectively responding only to linecurrents in the region of the phase-angle of fault-currents, means for promptly performing a protective relaying-operation under conditions involving a response of said directionally responsive relaying-means, blocking-means for blocking said protective relaying-operation in response to a predetermined response of said fault-responsive relaying-means and a simultaneous non-response of said directionally responsive means, and means for establishing a block-continuation which endures during the time when the line-current swings into the region of the phase-angle of fault-currents.

5. A fault-responsive protective relaying system for an alternating-current line, with provision for out-of-synchronism conditions, comprising one or more fault-responsive relayingmeans for selectively responding to certain faultcurrent conditions as distinguished from certain load-current conditions, directionally responsive relaying-means for selectively responding only to line-currents in the region of the phase-angle of fault-currents, means for promptly performing a protective relaying-operation in joint response to a predetermined response of one or more of said fault-responsive relaying-means and a response of said directionally responsive relaying-means, blocking-means for blocking said protective relaying-operation in response to a predetermined response of one or more ol said fault-responsive relaying-means and a simultaneous non-response of said directionally responsive means, and means for establishing a block-continuation which endures during the time when the line-current swings into the region of the phase-angle of fault-currents.

6. Means for detecting an out-of-synchronism condition in an alternating-current line, comprising abnormal-condition-responsive relayingmeans for selectively responding to an abnormal operating-condition as distinguished from certain load-current conditions of said line, directionally responsive relaying-means for selectively responding only to line-currents in the region of the phase-angle of fault-currents, and out-ofstep-responsive relaying-means for responding to a response of said abnormal-condition-responsive relaying-means, accompanied by a nonresponse of said directionally-responsive relaying means.

7. Means for detecting an out-of-synchronism condition in an alternating-current line, comprising two fault-responsive relaying-means for selectively responding respectively to a relatively mild and a relatively severe fault-current condition as distinguished from certain load-current conditions, directionally responsive relayingmeans for selectively responding only to linecurrents in the region of the phase-angle f fault-currents, and out-of-step-responsive relaying-means for responding to a response of said mild fault-responsive relaying-means, accomv12 panied by a non-response of said severe 'faultresponsive relaying-means, and further accompanied by a non-response of said directionallyresponsive relaying-means.

8. A fault-responsive protective relaying system for an alternating-current line, with provision for out-of-synchronism conditions, comprising two fault-responsive relaying-means for selectively responding respectively to a relatively mild and a relatively severe fault-current condition as distinguished from certain loadcurrent conditions, directionally responsive relaying-means for selectively respondingV only to line-currents in the region of the phaseangle of fault-currents, means for promptly performing a protective relaying-operation under conditions involving a response of said directionally responsive relaying-means, blocking-means for blocking said protective relaying-operation in response to a response of said mild fault-responsive relaying-means, accompanied by a non-response of said severe fault-responsive relaying-means, and further accompanied by a non-response of said directionally-responsive relaying-means, and means for establishing a block-continuation which endures during the time when the line-current swings into the region of the phase-angle oi fault-currents.

9. The invention as dened in claim 1, characterized by said directionally responsive relaying-means comprising two diiierently biased directional elements, one having a zero-torque angle at a line-current phase-angle slightly smailer than the fault-current phase-angle, and the other having a zero-torque angle at a linecurrent phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only'when the linecurrent has a phase-angle between the two zerotorque angles.

10. The invention asdened in claim 2, characterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a zero-torque angle at a line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two zero-torque angles.

1l. The invention as dened in claim 3, characterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a Zero-torque angle at a line-current rphase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two Zero-torque angles.

l2. The invention as defined in claim 4, charac- Vterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a Zero-torque angle at a line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle ata line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two zero-torque angles.

13. The invention as defined in claim 5, characterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a zero-torque angle at a line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two .Zero-torque angles.

14. The invention as dened in claim 6, characterized by said directionally responsive relayingmeans comprising two diierently biased directional elements, one having a Zero-torque angle at a, line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two zero-torque angles.

15. The invention as defined in claim 7, characterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a zero-torque angle at a, line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line-current has a phase-angle between the two zero-torque angles.

16. The invention as defined in claim 8, characterized by said directionally responsive relayingmeans comprising two differently biased directional elements, one having a Zero-torque angle at a line-current phase-angle slightly smaller than the fault-current phase-angle, and the other having a zero-torque angle at a line-current phase-angle slightly larger than the fault-current phase-angle, whereby both directional elements will respond only when the line current has a phase-angle between the two zero-torque angles.

EDWIN L. HARDER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,095,117 Banker et al Oct. 5, 1937 2,303,133 Neher Nov. 24, 1942 2,310,065 Crary Feb. 2, 1943 2,386,209 Goldsborough Oct. 9, 1945 2,405,079 Warrington July 30, 1946 FOREIGN PATENTS Number Country Date 527,343 Great Britain Oct. 7, 1940 

